The present invention relates to methods and apparatus for securely transmitting and processing digital image data. The invention provides for decomposing, compressing, and scrambling digital image data and forwarding the decomposed, compressed and scrambled image data to a destination where the data is decompressed, re-composed, and descrambled prior to display. In particular, digital image data is scrambled before or after being compressed with, for example, a lossy image compression algorithm. The image data is subsequently descrambled after being decompressed and prior to display such that unauthorized use of the image content is made more difficult. The invention can be used, e.g., in conjunction with most standard block-based image compression algorithms such as JPEG as well as some types of wavelet transform based systems.
Many of the existing and most useful compression techniques for digital images do not work on random or encrypted data. These techniques take advantage of spatial coherence of adjacent pixels and thus they need a clear, unencrypted version of the picture to work with. Also, common decryption algorithms cannot recover a data stream where the exact bit patterns have been altered by these lossy image compression and decompression algorithms.
Thus, the order of processing the image data at the viewing destination is typically dictated to be decryption first, followed by decompression, and finally display. The existing methods do not provide the combination of efficient decryption with efficient decoding of compression techniques applied to the digital image data. The fact that there is a decrypted, but still compressed copy of the digital image data at some point in the playback system makes a tempting target for pirates. For example, it is much easier to tap into a data stream of 10 to 50 Mbytes per second of compressed motion picture image data than it would be to tap and record the uncompressed stream of up to 800 Mbytes per second.
It would be very desirable to have a system where the image data is instead decrypted after being decompressed and where decryption is the last step prior to display of the image. Even more desirable is to have the decryption process integrated with the actual display device. The present invention provides the above and other advantages. Corresponding methods and apparatus are provided.
The present invention relates to methods and apparatus for securely transmitting and processing digital image data for display. The invention provides for decomposing, compressing, and scrambling digital image data and forwarding the decomposed, compressed and scrambled image data to a destination where it is decompressed, re-composed, and descrambled prior to display. In particular, digital image data is scrambled before or after being compressed with a lossy image compression algorithm and is subsequently descrambled only after being decompressed and just prior to display.
The invention is described for use with digital image data (e.g., motion picture data) which can be compressed using frequency decomposition techniques. However, those skilled in the art will appreciate that the invention is applicable to other types of data and compression techniques, such as audio data compressed using the MP3 technique. The invention can also be used in connection with any type of data that can be decomposed into frequency components. For example, the invention is also applicable to image-like types of data, such as radar maps, weather maps, seismic data, and the like.
Further, although the invention is described herein as providing for enhanced security of the transmitted data by descrambling the data just prior to display, those skilled in the art will appreciate that the invention may be utilized to secure the transmission of data to any type of destination, whether for storage, display, re-transmission, or the like.
In a particular embodiment of the invention, digital image data is decomposed into low and high spatial frequency components. The low frequency components are scrambled and the high frequency components are compressed. The scrambling step may take place at any point in the sequence; prior to, between, or after the steps of decomposition and compression. The steps of decomposing the image data, scrambling the low frequency components, and compressing the high frequency components are performed at an origination site by an encoding device. The compressed high frequency components and the scrambled low frequency components are transmitted from the origination site to a viewing destination. At the viewing destination, the compressed high frequency components are decompressed by reversing the compressing step. Decompression is performed by a decompression device. The decompressed high frequency components and the scrambled low frequency components are re-composed into an image at the viewing destination and the low frequency components are descrambled at a descrambling device. After descrambling, the image is displayed by a display device.
The low frequency components may be descrambled prior to display of the image at a descrambling device which is associated with the display device.
Alternatively, the descrambing device may be integral to the display device. In addition, the decompression device may also be integrated with the display device, such that decompression and descrambling take place prior to display.
The high frequency components may be compressed using quantization, entropy encoding, encoding of repeating values or patterns of values, or any other suitable compression technique. Alternatively, the high frequency components may be compressed utilizing a lossy compression algorithm.
The image may be decomposed into high and low spatial frequency components using a wavelet transform on the image, a discrete cosine transform (DCT), or other suitable decomposition techniques.
The low frequency components may be scrambled by the addition of a spatial noise function. Descrambling of the low frequency components is accomplished by subtracting a spatial noise function from the low frequency components. The spatial noise function may be (1) a pre-selected pattern of values known to both the scrambling and descrambling steps; (2) the output or a function of the output of a pseudo-random number generator based on a key known to both the scrambling and descrambling steps; (3) the output or a function of the output of a cryptographic block cipher algorithm based on a key known by both the scrambling and descrambling steps; (4) the output or a function of the output of a cryptographic key-pair encryption/decryption algorithm where one key is known to the scrambling step and the matching key is known to the descrambling step; or (5) any other suitable spacial noise function.
In a further embodiment, the spatial noise function is generated at the origination site and then securely transmitted to the viewing destination.
In another embodiment, scrambling of the low frequency components takes place prior to the step of decomposing the image into high and low frequency components.
In an alternate embodiment, scrambling of the low frequency components comprises encrypting the low frequency components. The low frequency components are descrambled by decrypting the encrypted low frequency components. The compressed high frequency components may be transmitted from the origination site to the viewing destination via a first communication channel and the encrypted low frequency components may be transmitted from the origination site to the viewing destination via a second communication channel.
In a further embodiment, the low frequency components may be compressed prior to being transmitted to the viewing destination. The low frequency components may be compressed in the same manner as the high frequency components. The compressed low frequency components may then be decompressed at the viewing destination by reversing the compressing step.
The low frequency components may also be compressed prior to or after being scrambled.